Keep common js functions in a file to be used throughout application

I have Rails app using Asset Pipeline. There are many js files associated with different parts of the app. To keep it DRY I want to start pulling some of the repetitive code into a file and use those methods throughout the app. What I am attempting right now isn't working.

common.js.coffee

common =
some_commonly_used_method: ->
// code

Some_other_page_speciific_file.js.coffee

common.some_commonly_used_method()

browser console when I load the page

Uncaught ReferenceError: common is not defined

What do I need to do to have common.whatever available throughout the app?